Power factor is important to utilities who deliver electrical power to customers. For two loads that require the same level of real power, the load with the better power factor actually demands less current from the utility. A load with a 1.0 power factor requires the minimum amount of current from the utility. Utilities may offer a reduced rate to customers with high power factor loads.
A poor power factor may be due to a phase difference between voltage and current. Power factor can also be degraded by distortion and harmonic content of the current. In some cases, distorted current waveforms tend to increase the harmonic energy content, and reduce the energy at the fundamental frequency. For a sinusoidal voltage waveform, only the energy at the fundamental frequency may transfer real power to a load. Distorted current waveforms can result from non-linear loads such as rectifier loads. Rectifier loads may include, for example, diodes such as LEDs, for example.
LEDs are widely used device capable of illumination when supplied with current. For example, a single red LED may provide a visible indication of operating state (e.g., on or off) to an equipment operator. As another example, LEDs can be used to display information in some electronics-based devices, such as handheld calculators. LEDs have also been used, for example, in lighting systems, data communications and motor controls.
Typically, an LED is formed as a semiconductor diode having an anode and a cathode. In theory, an ideal diode will only conduct current in one direction. When sufficient forward bias voltage is applied between the anode and cathode, conventional current flows through the diode. Forward current flow through an LED may cause photons to recombine with holes to release energy in the form of light.
The emitted light from some LEDs is in the visible wavelength spectrum. By proper selection of semiconductor materials, individual LEDs can be constructed to emit certain colors (e.g., wavelength), such as red, blue, or green, for example.
In general, an LED may be created on a conventional semiconductor die. An individual LED may be integrated with other circuitry on the same die, or packaged as a discrete single component. Typically, the package that contains the LED semiconductor element will include a transparent window to permit the light to escape from the package.
The applicant's U.S. Ser. Nos. 12/785,498 and 12/824,215 addressed these concerns by providing a plurality of circuits that conditioned current from an AC input that was compatible with dimming circuits and devices and those disclosures are incorporated in full herein. While such circuits are effective at solving previous problems in the art, improvements to the circuits are still desired. Specifically, the circuits provided as shown for example only in FIG. 23 provide what is considered a dead time at zero cross. Specifically, as voltage and current go from a negative quadrant to a positive quadrant, and vice versa, or even with a waveform existing entirely in the positive quadrant, as the waveform approaches the X axis or zero cross, the current flattens at zero into and out of the zero cross by the voltage waveform. In this manner a period of zero current or dead time is presented in the circuit at the zero cross.
This dead time is problematic when used in association with various dimmers or dimming circuits. In particular many dimmers, such as for example only, triac dimmers do not hold a charge and thus during this dead time there is no current making it difficult for the dimmer to initiate at zero cross when a reactive load is presented. Similar problems can also occur in IGBT type dimmers. As a result of difficulties in initiating in certain conditions, negative effects such as flicker and potentially perceptible flicker occurs. Thus a need in the art exists to minimize the negative effects of dead time at zero cross to improve performance of LED lighting assemblies.
Therefore a principle objective of the present invention is to provide dimming conditioning circuitry to improve performance of current conditioning in association with a circuit receiving an AC based input.